Yes, I have a friend with an HP dv6748us that does the same. (In fact just did it again yesterday.) Comes with VISTA & I set it on low (minimum) power setting & that seemed to help. Here is some of my related research (good luck):
Laptop turns on for a few seconds and then shuts down. No video appears on the screen.
Today I was able to fix a “dead” notebook simply by reseating connectors. The customer brought in Compaq nx5000 notebook with the following complaint:
“Laptop shuts down on power up. When the power button is pushed, the laptop flashes green lights for several seconds and then powers down. Unit will not stay on with battery or when plugged in”.
I plugged the AC adapter and tried to turn on the laptop. After I pushed on the power button, fans started spinning and were active for a few seconds and laptop just turned itself off. The video never came on. I tried to power it on for a few times with the same result.
Here is how I fixed it.
First of all I tried simple stuff: remove the battery and start the laptop with AC adapter plugged in, reseat and swap the memory module, remove the hard drive, the DVD drive, the wireless card. Nothing helped to start the laptop normally. After that I went a little bit further. I opened up the laptop case, removed the LCD screen assembly and reseated the video card and… Surprise, surprise, the laptop started fine with an external monitor attached. Just in case I restarted it 3-4 times and each time I got video on the screen. After I assembled everything back, one more surprise was waiting for me. The laptop failed to boot again with the same symptoms. So, the only part that I added before it failed was the LCD screen assembly. I unplugged the video cable from the system board and the laptop started fine again with the external monitor. Now I know that the problem is somewhere inside the display assembly (of course, if the video connector on the system board is fine). The next logical step would be opening up the LCD display assembly and check if all connectors are seated properly. Bingo!!! I wasn’t very surprised, but I was very happy. The video cable was half-way out from the connector on the back of the LCD screen. The laptop started perfectly fine as soon as I plugged the video cable back in place. Fixed!
That was my first experience when improperly plugged video cable prevented entire system from booting.